In ink-jet printing methods, small droplets of ink are allowed to fly onto a recording medium such as paper from fine nozzles and adhere to the recording medium, to form images or characters thereon. The ink-jet printing methods have becomes rapidly spread because of various advantages such as easiness of full coloration, low cost, non-contact with printed images or characters, etc.
In the ink-jet printing methods, although various advantages as described above are attained, the following problem tends to occur owing to the use of water as a main solvent for the ink for ink-jet printing. That is, when the water is contacted with a surface of an inside material of an ink-jet printer, in particular, a metal or ceramic material, etc., which is disposed at portions that tend to come into contact with the ink, the material tends to be oxidized so that metal ions or silicon ions contained therein tend to be eluted out in the ink, thereby causing such a problem that corrosion of the material gradually proceeds.
For example, WO 2009/035944A discloses an inkjet ink to be filled in a print head having a silicon dicing structure, in which by using a basic ink containing a trivalent metal ion, a metal ion-silicate complex is formed on a surface of silicon constituting the print head to thereby suppress elution of silica into the ink.
JP 2007-262326A discloses an aqueous pigment ink composition that includes a block polymer constituted of at least one hydrophilic block and at least one hydrophobic block and has a total metal content of not more than 100 ppm on the basis of the pigment, and is capable of satisfying not only color saturation and color density upon printing but also color image fastness.
JP 2008-69355A discloses an aqueous ink including a dispersion containing a pigment that is incorporated in a polymer to thereby render the pigment dispersible in water, and having a total polyvalent metal ion content of not more than 200 ppm, in which the ink causes less bleeding on a plain paper with a high color development, and exhibits not only sufficient color development but also good fixing property as well as excellent ejection property on an exclusive paper.
JP 2013-506730A discloses an ink composition including a pigment and an anionic charged polymer, and further including a dispersion of particles of an oxide of a polyvalent metal such as zirconium at a lower concentration than that of the pigment or anionic charged polymer, in which the pH of the ink composition is more than 4, and the polyvalent metal oxide particles have a negative zeta potential at the pH of the ink composition, and which is capable of providing an ink formulation having a higher polyvalent metal concentration.
JP 2004-217736A discloses an ink set constituted of at least one first ink including at least a first anionic or cationic colorant and fine particles of zirconia, etc., and at least one second ink including at least a second colorant having a reverse polarity to that of the first colorant, which has a high optical density and can produce images having a high printing quality without occurrence of bleeding.
JP 2003-138175A discloses a process for producing a dispersion ink for ink-jet printing using a wet stirred media mill and dispersing beads having a number of surface desorption of not more than 40 in which the ink is free from contamination with the beads and excellent in ejection property when used as an ink for ink-jet printing. In JP 2003-138175A, zirconia beads are illustrated as the dispersing beads.
However, the inks disclosed in WO 2009/035944A and JP 2008-69355 A contain the metals only in an ionic state. If the inks are used as an ink for ink-jet printing, it is not possible to attain a sufficient effect of suppressing corrosion of inside materials of a printer which come into contact with the inks, for example, such as a print head, for a long period of time. The ink disclosed in JP 2007-262326A is characterized by a less content of metals therein. However, if the ink contains the metals only in an ionic state, it is also not possible to attain a sufficient corrosion suppressing effect for a long period of time.